The present invention relates to optical systems. More specifically, it relates to automatic focus systems for automatically focussing an image of an object on a predetermined image plane.
There have been numerous efforts made in the past to provide means whereby a camera, either a still camera or a motion picture camera, may be made to focus automatically on the object which is being photographed. These have included means for evaluating the contrast of focussed and non-focussed images, means for measuring the angle of one or more beams of light projected from the camera to the object, means for analyzing the frequency components of an image as a function of focus, means for comparing the positions or the distribution of the light patterns of auxiliary images on separate, spaced single or multi-element light detectors, and mechanical or electromechanical means such as a pendulum actuated system. For one reason or another, none of the foregoing systems has provided to be entirely satisfactory for use in modern, relatively small, hand-held cameras.
For example, in those systems which provide means for evaluating the contrast components of the image, it is required that the analysis images achieve an exact focus in synchronism with exact focus of the principal image. If auxiliary lenses are used to provide the analysis images, these must be matched to the focal characteristics of the main lens. The same holds for systems which evaluate the frequency components of the analysis images. Those systems comparing the positions or the distribution of the light patterns of auxiliary images have exhibited deficiencies due to a lack of the necessary uniformity of the characteristics of the elements of their separate light detectors, particularly over a period of time, and due to a lack of adequate circuitry for processing the detector signals. These systems have also inherently been of such size as to require that the cameras containing them be unduly large. Those devices employing one or more light beams directed to the object, and those using a pendulum to effect automatic focus, require complex mechanical linkages.